Cell diversity and organisation

Question 1

How do cells become specialised?

Answer 1

• some genes are expressed while others are silenced due to differentiation
• cells produce proteins that determine their structure and function

Question 2

What is a transcription factor?

Answer 2

a protein controlling the transcription of genes so that only certain parts of the DNA are expressed in order to allow specialisation

Question 3

How do transcription factors work?

Answer 3

1) move from the cytoplasm into the nucleus

2) bind to promoter region upstream of target gene

3) makes it easier or more difficult for RNA polymerase to bind to gene (increasing or decreasing transcription rate)

Question 4

What is a stem cell?

Answer 4

undifferentiated cells that can divide indefinitely and turn into other specific cell types

Question 5

Name and define the 4 types of stem cells?

Answer 5

Totipotent = can develop into any cell type (including placenta and embryo)

Pluripotent = can develop into any cell type (except placenta and embryo)

Multipotent = can develop into a few different types of cells

Unipotent = can only develop into one cell type

Question 6

Suggest some uses of stem cells?

Answer 6

• repair damaged tissue
• drug testing on artificially grown tissues
• treating neurological diseases (e.g parkinson)
• researching developmental biology (e.g organ formation)

Question 7

Describe 2 groups of specialised cells in blood?

Answer 7

Erythrocytes
- red blood cells
- biconcave no nucleus
- lot’s of haemoglobin to carry oxygen

Leucocytes
- white blood cells
- lymphocytes to engulf foreign materials

Question 8

How do specialised cells in blood form?

Answer 8

multipotent stem cells in bone marrow

erythrocytes = with a short lifespan (unable to undergo mitosis as they have no nucleus)

lymphocytes = including neutrophil

Question 9

State the relationship between a system and specialised cells?

Answer 9

specialised cells - tissues that perform specific function - organs made of several tissue types - organ system

Question 10

Describe the structure of simple squamous epithelial cells?

Answer 10

• single smooth layer of squamous cells
• thin and flat with round nucleus
• fixed in place by basement membrane

Question 11

Describe the structure of ciliated epithelial cells?

Answer 11

• column shaped with surface projections called cilia
• cilia move in a synchronised pattern

Question 12

Describe the specialised structure of sperm?

Answer 12

• flagellum bound by plasma membrane propels cell
• spiral shaped mitochondria
• acrosome secretes enzyme to penetrate ovum coat
• haploid nucleus so fertilisation restores diploid chromosome number

Question 13

Describe the structure and function of palisade cells?

Answer 13

• specialised to absorb light energy for photosynthesis
• contain many chloroplast
• pack closely together

Question 14

Describe the structure and function of guard cells?

Answer 14

• form stomata
• when turgid stomata open, when flaccid stomata close
• walls are thickened by spirals of cellulose

Question 15

Describe the structure and function of root hair cells?

Answer 15

Function:
- absorb water and low-concentrated mineral ions from the soil

Structure:
- hair like projections increase SA for osmosis
- many mitochondria producing ATP for active transport

Question 16

What are meristems?

Answer 16

totipotent undifferentiated plant cells that can develop into various types of plant cells (including xylem and phloem)

Question 17

Describe the structure of a vascular bundle?

Answer 17

strands of vascular tissue containing xylem and phloem vessels that distribute water and organic substances around the plant

Question 18

Describe the structure of phloem of phloem tissue?

Answer 18

• sieve tube elements form a tube transporting sucrose in the dissolved form of sap
• companion cells involved in ATP production for active loading of sucrose into sieve tubes
• plasmodesmata are gaps between cell walls where the cytoplasm links allowing substances to flow

Question 19

Describe the structure of vessel elements in xylem tissue?

Answer 19

lignified secondary walls for mechanical strength and waterproofing with perforated end walls for rapid water flow

Question 20

Describe the structure of tracheids in xylem tissue?

Answer 20

tapered ends for close packing, pits for lateral water movement and contain no nucleus or cytoplasm

Question 21

Describe the structure of cartilage?

Answer 21

• avascular smooth elastic tissue which produces extensive extracellular matrix (ECM)
• ECM mainly contains collagen and proteoglycan

Question 22

Name 3 types of muscle in the body and where they are located?

Answer 22

cardiac = in the heart

smooth = walls of blood vessels and intestines

skeletal = attached to incompressible skeleton by tendons

Question 23

Describe the structure of skeletal muscle?

Answer 23

• cells form bundles of parallel muscle fibres called myofibrils
• arrangement ensures no weakness points in the cell
• bundles surrounded by loose connective tissue with many capillaries